Power amplifier device

ABSTRACT

A power amplifier device includes: a first power supply terminal for inputting a first power supply voltage; a first transistor for power amplification that (i) includes a first gate to which a bias voltage is applied, and (ii) is supplied with power from the first power supply terminal; a second power supply terminal for inputting a second power supply voltage lower than the first power supply voltage; a second transistor for monitoring that (i) includes a second gate to which the bias voltage is applied, (ii) is supplied with power from the first power supply terminal or the second power supply terminal, and (iii) imitates an operation of the first transistor; and a bias circuit that is supplied with power from the second power supply terminal and generates and adjusts the bias voltage according to a drain current or a source current of the second transistor.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. § 371 ofInternational Patent Application No. PCT/JP2021/015035, filed on Apr. 9,2021, which in turn claims the benefit of Japanese Application No.2020-080183, filed on Apr. 30, 2020, the entire disclosures of whichApplications are incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to power amplifiers and, for example, apower amplifier device including a bias circuit that adjusts a biasvoltage.

BACKGROUND ART

Mobile phone base stations etc. of recent years have required high-powerand high-efficiency power amplifier devices. High-electron mobilitytransistors (HEMTs) including a nitride semiconductor such as galliumnitride (GaN) or laterally-diffused metal-oxide semiconductor (LDMOS)transistors including a silicon-based semiconductor are capable ofperforming a high voltage operation and a high current density operationand are suitable for high-power power amplifier devices.

On the other hand, massive multiple-input and multiple-output (MIMO)that uses a large number of power amplifier devices and antenna devicesin a high frequency band (e.g., 3 GHz or higher) has been examined tospeed up signal transmission and reduce interference in signaltransmission. Since a large number of power amplifier devices areinstalled for one base station, there has been a demand for downsizingof power amplifier devices and reduction of the number of requiredadjustments.

Regarding the downsizing of the power amplifier devices and thereduction of the number of the required adjustments, Patent Literature(PTL) 1 discloses a bias circuit that monitors a drain current of atransistor for power amplification and adjusts a bias voltage.

CITATION LIST Patent Literature

[PTL 1] Japanese Unexamined Patent Application Publication No.2007-19631

SUMMARY OF INVENTION Technical Problem

According to the technique as disclosed by PTL 1, however, when atransistor for power amplification such as an HEMT or an LDMOStransistor is operated at a high voltage, the high voltage is alsoapplied to a bias circuit. As a result, the bias circuit consumes alarger amount of power. Moreover, the bias circuit need include ahigh-withstand-voltage element, and the costs are a big challenge.

In view of this, the present disclosure has an object to provide a poweramplifier device that solves the above problems, reduces powerconsumption, and cuts costs.

Solution to Problem

In order to achieve the above object, a power amplifier device accordingto one aspect of the present disclosure includes: a first power supplyterminal for inputting a first power supply voltage; a first transistorfor power amplification that (i) includes a first gate to which a biasvoltage is applied, and (ii) is supplied with power from the first powersupply terminal; a second power supply terminal for inputting a secondpower supply voltage lower than the first power supply voltage; a secondtransistor for monitoring that (i) includes a second gate to which thebias voltage is applied, (ii) is supplied with power from the firstpower supply terminal or the second power supply terminal, and (iii)imitates an operation of the first transistor; and a bias circuit thatis supplied with power from the second power supply terminal andgenerates and adjusts the bias voltage according to a drain current or asource current of the second transistor.

Advantageous Effects of Invention

The power amplifier device according to the present disclosure iscapable of reducing power consumption and cutting costs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a circuit diagram illustrating one configuration example of apower amplifier system including a power amplifier device according toEmbodiment 1.

FIG. 1B is a circuit diagram illustrating another configuration exampleof a power amplifier system including a power amplifier device accordingto Embodiment 1.

FIG. 2 is a circuit diagram illustrating one configuration of a biascircuit according to Embodiment 1.

FIG. 3 is a circuit diagram illustrating one configuration of a poweramplifier device according to Embodiment 1.

FIG. 4 is a diagram illustrating an example of setting a supply voltageby a power amplifier device according to Embodiment 1.

FIG. 5 is a circuit diagram illustrating a variation of a bias circuitaccording to Embodiment 1.

FIG. 6 is a circuit diagram illustrating one configuration example of apower amplifier system including a power amplifier device according toEmbodiment 2.

FIG. 7 is a circuit diagram illustrating one configuration of a biascircuit according to Embodiment 2.

FIG. 8A is a circuit diagram illustrating one configuration example of apower amplifier system including a power amplifier device according toEmbodiment 3.

FIG. 8B is a circuit diagram illustrating another configuration exampleof a power amplifier system including a power amplifier device accordingto Embodiment 3.

FIG. 9 is a circuit diagram illustrating a variation of a bias circuitaccording to Embodiment 3.

FIG. 10 is a circuit diagram illustrating one configuration of a poweramplifier device according to Embodiment 4.

DESCRIPTION OF EMBODIMENTS

Hereinafter, power amplifier devices of the present disclosure will bedescribed with reference to the drawings. However, detailed descriptionmay be omitted. For example, detailed description of well-known matterand overlapping description of identical elements may be omitted.Moreover, the respective figures are not necessarily preciseillustrations. These are to avoid making the subsequent descriptionverbose, and thus facilitate understanding by a person skilled in theart.

It should be noted that each of embodiments described below shows onespecific example of the present disclosure. The numerical values,shapes, materials, constituent elements, the arrangement and connectionof the constituent elements, etc. shown in the following embodiments aremere examples, are designed to help a person skilled in the art tosufficiently understand the present disclosure, and are not intended tolimit the subject matter of the claims.

Embodiment 1

Hereinafter, power amplifier systems each including a power amplifierdevice according to Embodiment 1 will be specifically described withreference to FIG. 1A to FIG. 4.

FIG. 1A is a circuit diagram illustrating one configuration example of apower amplifier system including a power amplifier device according toEmbodiment 1.

In FIG. 1A, the power amplifier system includes: power amplifier device100 that amplifies radio-frequency (RF) input signals into RF outputsignals; and power supply circuit 900 that supplies power to poweramplifier device 100. The power amplifier system is used for, forexample, mobile phone base stations or satellite communication basestations. It should be noted that the power amplifier system is notlimited to the base stations, and may be used for, for example, radartransmitters, wireless power transmitters, microwave ovens, andmicrowave heating devices.

Power amplifier device 100 includes, as external input-output terminals,an IN terminal, an OUT terminal, a VDD terminal, a VBB terminal, a VGGterminal, and a GND terminal. In addition, power amplifier device 100includes, for example, first transistor 101 for power amplification,bias circuit 120, capacitors 102 and 105, and inductors 103 and 104.

The IN terminal is a terminal that is connected to the gate of firsttransistor 101 via capacitor 102 and to which RF input signals areinputted.

The OUT terminal is a terminal that is connected to the drain of firsttransistor 101 via capacitor 105 and from which RF output signals areoutputted.

The VDD terminal is a terminal that is connected to the drain of firsttransistor 101 via inductor 104 and is for inputting first power supplyvoltage VDD. Specifically, the VDD terminal is a terminal for supplyingpower to first transistor 101 from power supply circuit 900 using firstpower supply voltage VDD. Moreover, the VDD terminal is also referred toas a first power supply terminal.

The VBB terminal is a terminal for inputting second power supply voltageVBB lower than first power supply voltage VDD. Specifically, the VBBterminal is a terminal for supplying power to bias circuit 120 frompower supply circuit 900 using second power supply voltage VBB.Moreover, the VBB terminal is also referred to as a second power supplyterminal.

The VGG terminal is a terminal for inputting third power supply voltageVGG for generating bias voltage. Specifically, the VGG terminal is aterminal for supplying power to bias circuit 120 from power supplycircuit 900 using third power supply voltage VGG. Third power supplyvoltage VGG is used for generating bias voltage VBIAS. Moreover, the VGGterminal is also referred to as a third power supply terminal.

The GND terminal is a terminal for grounding a GND line or a GND wiringlayer that is a reference potential inside power amplifier device 100.

It should be noted that although the terminals such as the VDD terminaland the VGG terminal differ in form depending on a mounting form of thepower amplifier device, examples of the terminals include a lead pin, aleadless pin, a wire-bonding pad, a solder ball pad, and a connector.

First transistor 101 amplifies RF input signals inputted from the INterminal via capacitor 102, and outputs RF output signals to the OUTterminal via capacitor 105. First transistor 101 has the gate to whichbias voltage VBIAS is applied from bias adjustment circuit 150 viainductor 103 to be gate-biased. First transistor 101 has the drain towhich first power supply voltage VDD is applied from power supplycircuit 900 via inductor 104. First transistor 101 has the source thatis grounded. It should be noted that the source, drain, and gate offirst transistor 101 can be referred to as a first source, a firstdrain, and a first gate, respectively. In addition, a source current, adrain current, and a gate current of first transistor 101 can bereferred to as a first source current, a first drain current, and afirst gate current, respectively.

Bias circuit 120 is supplied with power from the second power supplyterminal, and generates and adjusts bias voltage VBIAS according to adrain current or a source current of second transistor 121. For thisreason, bias circuit 120 includes, a Vbb terminal, a Vgg terminal, and aVBIAS terminal as input-output terminals. The Vbb terminal is connectedto the second power supply terminal, that is, the VBB terminal. The Vggterminal is connected to the third power supply terminal, that is, theVGG terminal. The VBIAS terminal is connected to inductor 103. Biascircuit 120 includes, for example, second transistor 121, currentsensing resistor 122, and bias adjustment circuit 150.

Second transistor 121 is a transistor for monitoring that imitatesoperations of first transistor 101. The operations imitated by secondtransistor 121 are mainly operations of first transistor 101 relating todirect current behavior. For this reason, bias voltage VBIAS is appliedto the gate of second transistor 121 from bias adjustment circuit 150.Second transistor 121 has the source that is grounded. In other words, agate voltage of second transistor 121 is biased with bias voltage VBIASthat is the same direct-current voltage as first transistor 101. Itshould be noted that the source, drain, and gate of second transistor121 can be referred to as a second source, a second drain, and a secondgate, respectively. In addition, a source current, a drain current, anda gate current of second transistor 121 can be referred to as a secondsource current, a second drain current, and a second gate current,respectively. As an imitation of an operation of first transistor 101,second transistor 121 causes a second drain current corresponding to afirst drain current to flow through the second drain. It should be notedthat the expression “a second drain current corresponding to a firstdrain current” means that a second drain is substantially proportionalto a first drain current, and need not be completely proportional to thesame.

Current sensing resistor 122 is a resistor for sensing a drain currentof second transistor 121, and is, for example, a high-precision resistorhaving a small manufacturing variation in resistance value and a smalltemperature fluctuation. Current sensing resistor 122 has one of twoterminals that is connected to the drain of second transistor 121, andthe other of the two terminals that is connected to the Vbb terminal.

Bias adjustment circuit 150 includes current sensing amplifier 160connected to the both ends of current sensing resistor 122, voltagesetting circuit 170 connected to the Vgg terminal and inductor 103, etc.Current sensing amplifier 160 amplifies a voltage between the both endsof current sensing resistor 122, and outputs drain current informationof second transistor 121 to voltage setting circuit 170. For example,drain current information is a current value or a voltage valuesubstantially proportional to a drain current of second transistor 121.

Voltage setting circuit 170 sets and adjusts bias voltage VBIAS, basedon the drain current information of second transistor 121.

Power supply circuit 900 generates and supplies first power supplyvoltage VDD, second power supply voltage VBB, and third power supplyvoltage VGG to power amplifier device 100.

It should be noted that second transistor 121 may be disposed outsidebias circuit 120 in FIG. 1A. FIG. 1B shows a configuration example ofthis case. Power amplifier device 100 s shown by FIG. 1B differs frompower amplifier device 100 shown by FIG. 1A in that second transistor121 is disposed not inside but outside bias circuit 120 s. These poweramplifier devices are identical except for this difference.

Next, a configuration example of bias circuit 120 will be described.

FIG. 2 is a circuit diagram illustrating one configuration of biascircuit 120 according to Embodiment 1. In particular, the figure is acircuit diagram illustrating one example of detailed configurations ofcurrent sensing amplifier 160 and voltage setting circuit 170 shown byFIG. 1A.

Current sensing amplifier 160 includes NPN transistor 161, PNPtransistor 162, resistors 163 and 164, etc. PNP transistor 162 has thebase to which reference voltage Vref obtained by resistors 163 and 164resistively dividing second power supply voltage VBB from the Vbbterminal is inputted. PNP transistor 162 has the emitter to which anemitter voltage of NPN transistor 161 is inputted. Since a voltageobtained by subtracting the amount of voltage drop by current sensingresistor 122 from second power supply voltage VBB is applied to the baseof NPN transistor 161, an emitter voltage and a collector current of PNPtransistor 162 decrease with a decrease in voltage drop by currentsensing resistor 122. To put it another way, the collector current ofPNP transistor 162 decreases with an increase in drain current of secondtransistor 121. A collector current of PNP transistor 162 is one exampleof the above-described drain current information.

Voltage setting circuit 170 includes resistors 171 and 172 etc. Resistor171 is connected to the collector of PNP transistor 162 and resistor172. Resistor 172 has one of two terminals that is connected to the Vggterminal, and the other of the two terminals that is connected toresistor 171. The connecting point between resistors 171 and 172 isconnected to the gate of second transistor 121. Resistors 171 and 172performs current-to-voltage conversion on the collector current of PNPtransistor 162 to generate bias voltage VBIAS. Bias voltage VBIASdecreases with a decrease in collector current of PNP transistor 162.The decrease in bias voltage VBIAS leads to a decrease in drain currentof second transistor 121. When the drain current of second transistor121 decreases to be less than a predetermined current value, biasvoltage VBIAS rises.

As stated above, bias adjustment circuit 150 including current sensingamplifier 160 and voltage setting circuit 170, and current sensingresistor 122 constitute a feedback control circuit that adjusts a draincurrent of second transistor 121 to a predetermined current value.

Next, a configuration example of power amplifier device 100 including asemiconductor substrate will be described.

FIG. 3 is a circuit diagram illustrating power amplifier device 100 t asone configuration of power amplifier device 100 according toEmbodiment 1. In particular, the figure is a circuit diagramillustrating a configuration when portions of power amplifier device 100shown by FIG. 1A are disposed on two semiconductor substrates.

Power amplifier device 100 t includes first semiconductor substrate 190and second semiconductor substrate 191. Some of the constituent elementsof bias circuit 120 shown by FIG. 1A are separately disposed on firstsemiconductor substrate 190 and second semiconductor substrate 191.Moreover, first semiconductor substrate 190 and second semiconductorsubstrate 191, together with current sensing resistor 122, capacitors102 and 105, and inductors 103 and 104, are mounted on a submountsubstrate such as multilayer resin substrate to form power amplifierdevice 100 t. In other words, power amplifier device 100 t may beconfigured as a submount substrate.

First semiconductor substrate 190 is, for example, a gallium nitride(GaN) semiconductor substrate disposed on a silicon (Si) substrate or asilicon carbide (SiC) substrate etc., and includes a VG1 terminal, a VG2terminal, a VD1 terminal, and a VD2 terminal. First transistor 101 andsecond transistor 121 are disposed on first semiconductor substrate 190.First transistor 101 and second transistor 121 are each a normally-ontransistor of HEMT type. First transistor 101 has, for example, gatewidth Wg1 of 3 mm. Second transistor 121 has, for example, gate widthWg2 of 0.4 mm. Second transistor 121 differs from first transistor 101in gate width, but has the same device architecture as first transistor101. First transistor 101 has the gate to which bias voltage VBIAS isapplied via inductor 103 and the VG1 terminal to be gate-biased, andamplifies RF input signals inputted from the IN terminal. Firsttransistor 101 has the drain to which first power supply voltage VDD isapplied via inductor 104 and the VD1 terminal, and outputs, to the OUTterminal, output signals obtained by amplifying the RF input signals.Second transistor 121 has the gate to which bias voltage VBIAS isapplied via the VG2 terminal. Second transistor 121 has the drain towhich second power supply voltage VBB is applied via current sensingresistor 122 and the VD2 terminal. Since first transistor 101 and secondtransistor 121 are subjected to the same change in temperature on firstsemiconductor substrate 190, second transistor 121 can more accuratelymonitor a variation in characteristics of first transistor 101 due tothe change in temperature. For example, it is possible to moreaccurately reflect a variation in first drain current due to a change intemperature in a second drain current.

Second semiconductor substrate 191 is, for example, a gallium arsenide(GaAs) semiconductor substrate and includes a Vbb terminal, a Vbdterminal, a Vgg terminal, and a VBIAS terminal. Current sensingamplifier 160 and voltage setting circuit 170 are disposed on secondsemiconductor substrate 191, and this configuration is equivalent tobias adjustment circuit 150 shown by FIG. 1A. A voltage between the bothends of current sensing resistor 122 is inputted to current sensingamplifier 160 via the Vbb terminal and the Vbd terminal, and currentsensing amplifier 160 outputs drain current information of secondtransistor 121 to voltage setting circuit 170. Voltage setting circuit170 adjusts bias voltage VBIAS, based on the drain current informationof second transistor 121, and outputs adjusted bias voltage VBIAS viathe VBIAS terminal.

The following describes operations of power amplifier device 100 thusconfigured according to Embodiment 1. First transistor 101 for poweramplification amplifies RF input signals inputted to the gate of firsttransistor 101 from the IN terminal, and outputs RF output signals tothe OUT terminal connected to the drain of first transistor 101. Biascircuit 120 applies bias voltage VBIAS to the gate of first transistor101 so that first transistor 101 performs class AB operation. Biasvoltage VBIAS is, for example, approximately −2.5 V. Power supplycircuit 900 applies first power supply voltage VDD to the drain of firsttransistor 101 to supply power for power amplification. First powersupply voltage VDD is, for example, 40 V. It should be noted that due tocapacitors 102 and 105 connected to the gate or the drain,radio-frequency signals pass from the IN terminal to the OUT terminal,but a direct current does not flow from the IN terminal to the OUTterminal. Moreover, due to inductors 103 and 104 connected to the gateor the drain, a direct current flows from bias circuit 120 or powersupply circuit 900, but radio-frequency signals are not transmitted tobias circuit 120 or power supply circuit 900. Since no RF input signalsfrom the IN terminal also flow into second transistor 121, secondtransistor 121 imitates not an operation of amplifying an RF inputsignal by first transistor 101 but a direct-current operation of firsttransistor 101. It should be noted that a means to block or reduceradio-frequency signals to bias circuit 120 or power supply circuit 900and to pass a direct-current voltage and a direct current need not beinductor 103, and such a means may be, for example, a low-pass filterincluding a resistor, a capacitor, etc.

The following describes operations of bias circuit 120 in detail. Biasvoltage VBIAS outputted from bias circuit 120 is set so that firsttransistor 101 performs class AB operation. Bias voltage VBIAS is set sothat a drain current of first transistor 101 when an RF input signal isin a no-signal state, that is, idle current Idq1 has a predeterminedvalue, for example, 75 mA (25 mA per gate width Wg=1 mm). Here,characteristics of first transistor 101, for example, threshold voltageand mutual conductance, vary due to a manufacturing variation ortemperature dependency. When bias voltage VBIAS has a fixed voltagevalue, idle current Idq1 varies due to a variation in characteristics offirst transistor 101. This causes the problem of varied powerefficiency, power gain, linearity, etc., which are main characteristicsof power amplifier device 100. For this reason, bias circuit 120 has afunction of adjusting bias voltage VBIAS so that idle current Idq1 has apredetermined value even when the characteristics of first transistor101 vary.

Power supply circuit 900 applies second power supply voltage VBB andthird power supply voltage VGG to bias circuit 120. Second power supplyvoltage VBB is, for example, 5 V, and third power supply voltage VGG is,for example, −5 V. Second transistor 121 is gate-biased at bias voltageVBIAS in the same manner as first transistor 101, and drain current Idq2flows as a second drain current through second transistor 121. Sinceinductor 103 does not input an RF input signal to second transistor 121,drain current Idq2 stays constant regardless of the RF input signal.Drain current Idq2 is substantially proportional to idle current Idq1 offirst transistor 101 and is, for example, 10 mA. It should be noted thatthe term “substantially proportional” means that drain currents of firsttransistor 101 and second transistor 121 have a substantiallyproportional relationship because (i) first transistor 101 and secondtransistor 121 are semiconductor devices, and (ii) it is rare that evenif the same drain voltage and gate voltage are applied to firsttransistor 101 and second transistor 121, drain currents of firsttransistor 101 and second transistor 121 have a complete proportionalrelationship. For this reason, detecting drain current Idq2 of secondtransistor 121 makes it possible to monitor idle current Idq1 of firsttransistor 101. Moreover, second transistor 121 has the same devicearchitecture as first transistor 101, is disposed on same firstsemiconductor substrate 190 as first transistor 101, and is contained inone package so that second transistor 121 operates in conjunction withthe variation in characteristics of first transistor 101 due to themanufacturing variation or the temperature dependency. It should benoted that first transistor 101 and second transistor 121 may bedisposed on different semiconductor substrates. In this case, firsttransistor 101 and second transistor 121 may be contained in the samepackage and thermally coupled.

FIG. 4 is a diagram illustrating an example of setting a supply voltageby power amplifier device 100 according to Embodiment 1. Morespecifically, (a) in FIG. 4 is a characteristic diagram whenpredetermined bias voltage VBIAS is applied to the gate of firsttransistor 101, the characteristic diagram having the horizontal axisand the vertical axis representing drain voltage VD1 and drain currentID1 of first transistor 101, respectively. (b) in FIG. 4 is acharacteristic diagram when predetermined bias voltage VBIAS is appliedto the gate of second transistor 121, the characteristic diagram havingthe horizontal axis and the vertical axis representing drain voltage VD2and drain current ID2 of second transistor 121, respectively.

First power supply voltage VDD is applied to the drain of firsttransistor 101. Then, as shown by (a) in FIG. 4, first transistor 101operates in a saturation region, and idle current Idq1 flows in firsttransistor 101. (a) in FIG. 4 shows an example in which first powersupply voltage VDD is 40 V, and idle current Idq1 is 75 mA.

In contrast, second power supply voltage VBB (=5 V) is applied to thedrain of second transistor 121. Then, as shown by (b) in FIG. 4, secondtransistor 121 operates in a saturation region, and drain current Idq2(=10 mA) flows in second transistor 121. (b) in FIG. 4 shows an examplein which second power supply voltage VBB is 5 V, and drain current Idq2is 10 mA.

When second transistor 121 also operates in the saturation region, adrain current ratio is a value close to a gate width ratio even if asupply voltage to the drain of first transistor 101 is significantlydifferent from a supply voltage to the drain of second transistor 121.Accordingly, second power supply voltage VBB may be set so that secondtransistor 121 operates in the saturation region. It should be notedthat even if second transistor 121 is made to operate in a linearregion, there is no problem as long as a drain current ratio can beobtained with a desired accuracy. Furthermore, strictly speaking, thedrain voltage of second transistor 121 is reduced to be lower thansecond power supply voltage VBB by voltage drop by current sensingresistor 122. For this reason, a resistance value of current sensingresistor 122 may be set low within an acceptable range of currentsensing accuracy to reduce voltage drop.

Current sensing resistor 122 is a resistor for sensing drain currentIdq2 of second transistor 121 and has, for example, a resistance of100Ω. For example, when drain current Idq2 of 10 mA flows, a voltagebetween the both ends (detection voltage Vdetect) of current sensingresistor 122 is 1.0 V.

Current sensing amplifier 160 causes resistors 163 and 164 toresistively divide second power supply voltage VBB to generate referencevoltage Vref. Resistors 163 and 164 have, for example, resistances of3.4 kΩ and 1.6 kΩ, respectively, and reference voltage Vref is 1.6 V.NPN transistor 161 and PNP transistor 162 pass a collector currentcorresponding to detection voltage Vdetect and reference voltage Vrefand output the collector current to voltage setting circuit 170.

Voltage setting circuit 170 causes resistors 171 and 172 to performcurrent-to-voltage conversion on the collector current of PNP transistor162 to generate bias voltage VBIAS. Resistors 171 and 172 both have, forexample, a resistance of 1 kΩ, and an intermediate potential between acollector voltage of PNP transistor 162 and third power supply voltageVGG is bias voltage VBIAS.

As stated above, when idle current Idq1 of first transistor 101decreases due to, for example, a change in temperature, drain currentIdq2 of second transistor 121 in a substantially proportionalrelationship with first transistor 101 decreases. A base voltage of NPNtransistor 161 rises, and the collector current of PNP transistor 162increases. Accordingly, bias voltage VBIAS rises, and drain current Idq2of second transistor 121 increases. Idle current Idq1 of firsttransistor 101 in the substantially proportional relationship withsecond transistor 121 also increases. Consequently, bias circuit 120 iscapable of operating to increase idle current Idq1 of first transistor101 for power amplification when idle current Idq1 decreases to be lessthan a predetermined current value due to the manufacturing variation orthe temperature dependency etc.

Contrary to the above description, when idle current Idq1 of firsttransistor 101 increases, a base voltage of NPN transistor 161 drops,and the collector current of PNP transistor 162 decreases. Accordingly,bias voltage VBIAS drops, and it is possible to decrease idle currentIdq1 of first transistor 101. Consequently, bias circuit 120 is capableof controlling bias voltage VBIAS according to an increase or decreasein idle current Idq1 of first transistor 101 for power amplification, tokeep idle current Idq1 constant.

As described above, the power amplifier device according to Embodiment 1is capable of monitoring idle current Idq1 of first transistor 101 forpower amplification and adjusting bias voltage VBIAS, to reduce avariation in idle current Idq1 due to the manufacturing variation or thetemperature dependency and to perform a predetermined class operation.Moreover, whereas it is possible to improve power efficiency byapplying, for example, 40 V to the drain of first transistor 101 tocause first transistor 101 to perform a high voltage operation, a supplyvoltage to be applied to bias circuit 120 is, for example, at most 5 V,and it is possible to reduce power consumption. Furthermore, biascircuit 120 can be formed of a low-withstand-voltage element except forsecond transistor 121, which can reduce manufacturing costs.

It should be noted that although first transistor 101 and secondtransistor 121 are each a transistor of HEMT type disposed on firstsemiconductor substrate 190, which is a gallium nitride (GaN)semiconductor substrate, in the present embodiment, first transistor 101and second transistor 121 may be each an LDMOS transistor disposed on asilicon (Si) semiconductor substrate. It should be noted that when firsttransistor 101 and second transistor 121 are each a normally-offtransistor, third power supply voltage VGG may be set to a ground levelor a positive voltage.

It should be noted that although bias adjustment circuit 150 is disposedon second semiconductor substrate 191, which is a gallium arsenide(GaAs) semiconductor substrate, in the present embodiment, biasadjustment circuit 150 may be disposed on a silicon (Si) semiconductorsubstrate. Moreover, bias adjustment circuit 150 may be disposed on thesame semiconductor substrate as second transistor 121. For example,first transistor 101 and second transistor 121 may each be a siliconLDMOS transistor that operates at a high voltage of at least 10 V, andbias adjustment circuit 150 may be a silicon complementary MOS (CMOS)circuit that operates at a low voltage of at most 10 V.

It should be noted that although current sensing resistor 122 is notdisposed on second semiconductor substrate 191 because current sensingresistor 122 has a big influence on a variation in idle current Idq1 offirst transistor 101 in the present embodiment, current sensing resistor122 may be disposed on second semiconductor substrate 191. Currentsensing resistor 122 may be disposed close to current sensing amplifier160 to offset the temperature dependency of transistors etc. in currentsensing amplifier 160. Moreover, current sensing resistor 122 may bedisposed on first semiconductor substrate 190. By disposing currentsensing resistor 122 close to first transistor 101 and changing aresistance value of current sensing resistor 122 dependent on atemperature of first transistor 101, idle current Idq1 of firsttransistor 101 may be caused to have temperature dependency. Forexample, by increasing the resistance value of current sensing resistor122 as first transistor 101 has a higher temperature, it is possible todecrease idle current Idq1, improve power efficiency, and reduce heatgeneration. Furthermore, resistance adjustment may be made by lasertrimming etc. in an inspection process etc. In addition, current sensingresistor 122 may be a variable resistor of which a user can adjust aresistance value.

It should be noted that although bias circuit 120 that senses the draincurrent of second transistor 121 using current sensing resistor 122 hasbeen described in the present embodiment, other current sensing methodsmay be used. For example, FIG. 5 shows, as a variation of bias circuit120, bias circuit 120 a including a current mirror circuit. Bias circuit120 a includes bias adjustment circuit 150 a including a current mirrorcomposed of p-type MOSFETs 151 and 152. The current mirror generates acurrent proportional to the drain current of second transistor 121, andcurrent sensing resistor 153 performs current-to-voltage conversion. Avoltage proportional to the drain current of second transistor 121 isinputted to current sensing amplifier 160, and the same advantageouseffect as the present embodiment is produced.

It should be noted that although the configuration including NPNtransistor 161 and PNP transistor 162 has been described as currentsensing amplifier 160 in the present embodiment, the configuration mayinclude an arithmetic circuit such as an operational amplifier.

It should be noted that power amplifier device 100 may contain amatching circuit for adjusting an impedance of the IN terminal or theOUT terminal to 50Ω etc. In addition, the matching circuit, togetherwith capacitors 102 and 105, inductors 103 and 104, etc., may bedisposed on first semiconductor substrate 190 on which first transistor101 is disposed, or may be disposed on second semiconductor substrate191 on which bias adjustment circuit 150 is disposed.

It should be noted that although the sources of first transistor 101 andsecond transistor 121 are grounded in the present embodiment, thesources may be grounded via a resistor or an inductor.

It should be noted that although the gate of first transistor 101 andthe gate of second transistor 121 are connected via inductor 103 in thepresent embodiment, a resistor or an inductor may be further insertedbetween the gate of first transistor 101 and the gate of secondtransistor 121. Moreover, a capacitor may be inserted between the gateof second transistor 121 and the GND to stabilize a gate voltage.Furthermore, a level shift circuit etc. may shift and input bias voltageVBIAS to the gate of second transistor 121. The level shift circuit mayadd a resistor in voltage setting circuit 170 to make it possible tosupply different bias voltages VBIAS to first transistor 101 and secondtransistor 121.

It should be noted that although first transistor 101 and secondtransistor 121 have the same device architecture in the presentembodiment, first transistor 101 and second transistor 121 may each havea different device architecture. For example, first transistor 101 andsecond transistor 121 may differ in a gate structure such as a gatelength.

It should be noted that although first power supply voltage VDD appliedfrom power supply circuit 900 is kept at 40 V in the present embodiment,first power supply voltage VDD may vary. For example, like an envelopetracking amplifier device, first power supply voltage VDD may be variedby an RF input signal. In this case, second power supply voltage VBB maybe a constant voltage or may be linked to first power supply voltageVDD.

As described above, power amplifier device 100 according to Embodiment 1includes: a first power supply terminal for inputting first power supplyvoltage VDD; first transistor 101 for power amplification that (i)includes a first gate to which bias voltage VBIAS is applied, and (ii)is supplied with power from the first power supply terminal; a secondpower supply terminal for inputting second power supply voltage VBBlower than first power supply voltage VDD; second transistor 121 formonitoring that (i) includes a second gate to which bias voltage VBIASis applied, (ii) is supplied with power from the first power supplyterminal or the second power supply terminal, and (iii) imitates anoperation of first transistor 101; and bias circuit 120 that is suppliedwith power from the second power supply terminal and generates andadjusts bias voltage VBIAS according to a drain current or a sourcecurrent of second transistor 121.

With this configuration, it is possible to reduce the power consumptionof bias circuit 120. In addition, it is possible to reduce costs becausebias circuit 120 can be formed of a low-withstand-voltage,general-purpose, low-cost element.

Here, second transistor 121 may be supplied with the power from thesecond power supply terminal.

With this configuration, it is possible to further reduce the powerconsumption of second transistor 121.

Here, bias circuit 120 may generate and adjust bias voltage VBIASaccording to the source current of second transistor 121.

With this configuration, it is possible to sense the source current as alower voltage value than a voltage value of the drain current, causebias circuit 120 to perform a lower voltage operation, and furtherreduce power consumption.

Moreover, power amplifier device 100 according to Embodiment 1 includes:a first power supply terminal for inputting first power supply voltageVDD; first transistor 101 for power amplification that includes a firstdrain supplied with power from the first power supply terminal, a firstsource that is grounded, and a first gate for inputting aradio-frequency signal; a second power supply terminal for inputtingsecond power supply voltage VBB lower than first power supply voltageVDD; and bias circuit 120 that applies bias voltage VBIAS to first gateof first transistor 101. Bias circuit 120 includes: second transistor121 for monitoring that (i) includes a second drain supplied with powerfrom the second power supply terminal, a second source that is grounded,and a second gate electrically connected to the first gate, and (ii)causes a second drain current to flow through the second drain, thesecond drain current corresponding to a first drain current flowingthrough the first drain; and bias adjustment circuit 150 that issupplied with the power from the second power supply terminal andadjusts the bias voltage according to the second drain current.

With this configuration, it is possible to reduce the power consumptionof bias circuit 120. In addition, it is possible to reduce costs becausebias circuit 120 can be formed of a low-withstand-voltage,general-purpose, low-cost element.

Here, second power supply voltage VBB may be set to a voltage at whichsecond transistor 121 operates in a saturation region.

With this configuration, by second transistor 121 operating in thesaturation region in which drain voltage dependency of second transistor121 is stable, it is possible to reduce differences in power supplyvoltage characteristics of first transistor 101 and second transistor121.

Here, second transistor 121 may be contained in the same package asfirst transistor 101.

With this configuration, since first transistor 101 and secondtransistor 121 are subjected to the same change in temperature in thepackage, second transistor 121 can more accurately monitor a variationin characteristics of first transistor 101 due to the change intemperature.

Here, second transistor 121 may be disposed on same first semiconductorsubstrate 190 as first transistor 101.

With this configuration, since first transistor 101 and secondtransistor 121 are subjected to the same change in temperature on firstsemiconductor substrate 190, second transistor 121 can more accuratelymonitor a variation in characteristics of first transistor 101 due tothe change in temperature.

Here, at least part of bias circuit 120 may be disposed on a differentsemiconductor substrate from second transistor 121.

With this configuration, since bias circuit 120 can be formed of, forexample, low-cost second semiconductor substrate 191 that is differentfrom first semiconductor substrate 190 including first transistor 101and second transistor 121, it is possible to further reduce costs.

Here, power amplifier device 100 may include current sensing resistor122 connected to the drain of second transistor 121; and a submountsubstrate on which the semiconductor substrate is mounted. Currentsensing resistor 122 may be mounted on the submount substrate.

With this configuration, it is easy to use, as current sensing resistor122, a resistance element more accurate in a variation or temperaturecharacteristics than a resistor disposed on the semiconductor substrate.Moreover, by disposing current sensing resistor 122 outside thesemiconductor substrate, it is possible to easily adjust a second draincurrent value at a manufacturing stage in which the semiconductorsubstrate is mounted on the submount substrate. Even when currentsensing resistor 122 is disposed outside the semiconductor substrate,the number of the terminals of first semiconductor substrate 190including first transistor 101 and second transistor 121 or the numberof the terminals of second semiconductor substrate 191 including currentsensing amplifier 160 and voltage setting circuit 170 is not increased.

Here, first transistor 101 and second transistor 121 may each be anitride semiconductor.

With this configuration, even if first transistor 101 and secondtransistor 121 are each a nitride semiconductor that performs a highfrequency and high voltage operation, bias circuit 120 can bemanufactured using low-withstand-voltage, general-purpose circuitcomponents.

Here, first transistor 101 and second transistor 121 may each be anLDMOS transistor.

With this configuration, even if first transistor 101 and secondtransistor 121 are each an LDMOS transistor that performs a highfrequency and high voltage operation, bias circuit 120 can bemanufactured using low-withstand-voltage, general-purpose circuitcomponents.

Embodiment 2

Next, a power amplifier system including a power amplifier deviceaccording to Embodiment 2 will be described with reference to FIG. 6 andFIG. 7.

Embodiment 2 describes a power amplifier device having an enablefunction. It should be noted that description overlapping Embodiment 1will be omitted.

FIG. 6 is a circuit diagram illustrating one configuration example of apower amplifier system including a power amplifier device according toEmbodiment 2. The power amplifier system shown by FIG. 6 differs fromthe power amplifier system shown by FIG. 1A including the poweramplifier device according to Embodiment 1 in including power amplifierdevice 200 instead of power amplifier device 100. The following mainlydescribes the differences. Power amplifier device 200 differs from poweramplifier device 100 shown by FIG. 1A in including bias circuit 220instead of bias circuit 120 and in that an EN terminal is added as anenable control terminal for controlling an active state and an inactivestate of a bias voltage. Bias circuit 220 includes bias adjustmentcircuit 250 comprising, for example, current sensing amplifier 260connected to the EN terminal of power amplifier device 200 via theEnable terminal, and voltage setting circuit 170.

It should be noted that as with in FIG. 1B, second transistor 121 may bedisposed outside bias circuit 220 in FIG. 6.

FIG. 7 is a circuit diagram illustrating one configuration of biascircuit 220 of the power amplifier device according to Embodiment 2.Bias circuit 220 differs from bias circuit 120 according to Embodiment 1shown by FIG. 2 in including an Enable terminal, inverter circuits 265and 266, and p-type MOSFET 267. The Enable terminal is connected to thegate of p-type MOSFET 267 via inverter circuits 265 and 266. Secondpower supply voltage VBB is applied to the source of p-type MOSFET 267.The drain of p-type MOSFET 267 is connected to a connecting pointbetween resistors 163 and 164 for generating reference voltage Vref.

The following describes operations of the power amplifier device thusconfigured according to Embodiment 2, mainly focusing on the enablefunction different from Embodiment 1.

Bias circuit 220 is capable of changing bias voltage VBIAS according toan EN terminal voltage of power amplifier device 200, to switch anoperation of first transistor 101 between an active state (ON state) andan inactive state (OFF state). When a high-level voltage, for example,3.3 V is applied to the EN terminal, an output of inverter circuit 265becomes a low level, an output of inverter circuit 266 becomes a highlevel, and second power supply voltage VBB is applied to the gate ofp-type MOSFET 267. p-type MOSFET 267 is normally OFF and non-conductive.Accordingly, when the high-level voltage is applied to the EN terminal,first transistor 101 and second transistor 121 are in the ON-state andoperate in the same manner as bias circuit 120 according to Embodiment1.

In contrast, when a low-level voltage, for example, 0 V is applied tothe EN terminal, an output of inverter circuit 265 becomes a high level,an output of inverter circuit 266 becomes a low level, and the gate ofp-type MOSFET 267 becomes a low level. When p-type MOSFET 267 becomesconductive, reference voltage Vref rises to the vicinity of second powersupply voltage VBB. When a collector current of PNP transistor 162sufficiently decreases, bias voltage VBIAS drops to the vicinity ofthird power supply voltage VGG, and first transistor 101 and secondtransistor 121 enter the OFF state. Accordingly, when the low-levelvoltage is applied to the EN terminal, power amplifier device 200 entersthe OFF state, and the power consumption is significantly reducedcompared to a case in which an RF input signal is in a no-signal state.

As stated above, as with Embodiment 1, since the power amplifier deviceaccording to Embodiment 2 includes the bias circuit capable of reducinga variation in drain current due to a manufacturing variation ortemperature dependency of first transistor 101 for power amplification,and is further capable of reducing a supply voltage to the bias circuit,it is possible to achieve a circuit configuration capable of powerconsumption reduction and cost reduction. Moreover, it is possible tocause power amplifier device 200 to enter the OFF state when poweramplification is unnecessary, making power consumption reductionpossible. Furthermore, it is possible to include the enable function byadding a small number of low-withstand-voltage elements, making itpossible to suppress an increase in cost.

It should be noted that the enable function is also effective when acommunication scheme such as time division duplex (TDD) switches betweentransmission and reception in the same frequency band on a per timebasis. For example, in the case of an amplifier device for transmission,it is easy to perform the switching by changing an EN terminal voltageto a high level at the time of transmission and to a low level at thetime of reception.

It should be noted that although an EN terminal voltage is caused tohave no influence on reference voltage Vref when the EN terminal voltageis at a high level, by configuring the enable control portion of currentsensing amplifier 260 using inverter circuits 265 and 266 and p-typeMOSFET 267 in the present embodiment, the enable control portion may beconfigured using a PNP transistor etc. In addition, an EN terminalvoltage may influence reference voltage Vref when the EN terminalvoltage is at a high level.

It should be noted that although the enable function is achieved byindirectly changing bias voltage VBIAS by changing reference voltageVref in the present embodiment, bias voltage VBIAS may be directlychanged.

As described above, power amplifier device 200 according to Embodiment 2includes an enable control terminal for controlling an active state andan inactive state of the bias voltage.

With this configuration, since the bias circuit can be formed of alow-withstand-voltage, general-purpose circuit element, it is possibleto easily implement the enable function by the enable control terminal.

Embodiment 3

Next, a power amplifier system including a power amplifier deviceaccording to Embodiment 3 will be described with reference to FIG. 8A.

Embodiment 3 describes a power amplifier device including a bias circuitthat senses a source current of a second transistor. It should be notedthat description overlapping Embodiment 1 will be omitted.

FIG. 8A is a circuit diagram illustrating one configuration example of apower amplifier system including a power amplifier device according toEmbodiment 3. The power amplifier system shown by FIG. 8A differs fromthe power amplifier system shown by FIG. 1A including the poweramplifier device according to Embodiment 1 in including power amplifierdevice 300 instead of power amplifier device 100. The following mainlydescribes the differences. Power amplifier device 300 differs from poweramplifier device 100 shown by FIG. 1A in including bias circuit 320instead of bias circuit 120. Bias circuit 320 has a Vdd terminal, a Vbbterminal, a Vgg terminal, and a VBIAS terminal and includes, forexample, second transistor 321, current sensing resistor 322, and biasadjustment circuit 350. Bias adjustment circuit 350 includes currentsensing amplifier 360 and voltage setting circuit 370. Second transistor321 is a transistor for monitoring a drain current of first transistor101 for power amplification. Second transistor 321 differs from secondtransistor 121 shown by FIG. 1A in having the drain connected to the Vddterminal and the source connected to current sensing resistor 322.Second transistor 321 has the source that is substantially grounded.Here, the term “substantially grounded” is not limited to mean thatsecond transistor 321 is directly grounded, and is intended to mean thatsecond transistor 321 has the source that is grounded via currentsensing resistor 322. This is because a resistance value of currentsensing resistor 322 is sufficiently small.

It should be noted that second transistor 321 may be disposed outsidebias circuit 320 in FIG. 8A. FIG. 8B shows a configuration example ofthis case. Power amplifier device 300 s shown by FIG. 8B differs frompower amplifier device 300 shown by FIG. 8A in that second transistor321 is disposed not inside but outside bias circuit 320 s. These poweramplifier devices are identical except for this difference.

The following describes operations of the power amplifier device thusconfigured according to Embodiment 3, mainly focusing on bias circuit320 different from Embodiment 1.

Power supply circuit 900 applies second power supply voltage VBB andthird power supply voltage VGG to bias circuit 320. Second power supplyvoltage VBB is, for example, 3.3 V, and third power supply voltage VGGis, for example, −5 V. Same bias voltage VBIAS as first transistor 101is applied to the gate of second transistor 321, and drain current Idq2flows through the drain of second transistor 321. Here, when secondtransistor 321 is a transistor of HEMT type or an LDMOS transistor,since almost no current flows between the gate and the drain or the gateand the source, source current Isq2 is substantially equal to draincurrent Idq2. Since inductor 103 does not input an RF input signal tosecond transistor 321, source current Isq2 stays constant regardless ofthe RF input signal. Source current Isq2 is substantially proportionalto idle current Idq1 of first transistor 101 and is, for example, 10 mA.It should be noted that the term “substantially proportional” means thatdrain currents and source currents of first transistor 101 and secondtransistor 321 have a substantially proportional relationship because(i) first transistor 101 and second transistor 321 are semiconductordevices, and (ii) it is rare that even if the same drain voltage andgate voltage are applied to first transistor 101 and second transistor321, drain currents and source currents of first transistor 101 andsecond transistor 321 have a complete proportional relationship. Forthis reason, detecting source current Isq2 of second transistor 321makes it possible to monitor idle current Idq1 of first transistor 101.Moreover, second transistor 321 may have the same device architecture asfirst transistor 101, be disposed on the same semiconductor substrate asfirst transistor 101, and be contained in one package so that secondtransistor 321 operates in conjunction with the variation incharacteristics of first transistor 101 due to a manufacturing variationor temperature dependency.

Current sensing resistor 322 is a resistor for sensing source currentIsq2 of second transistor 321 and has, for example, a resistance of 10Ω.For example, when source current Isq2 of 10 mA flows, a voltage betweenthe both ends (detection voltage Vdetect) of current sensing resistor322 is 0.1 V.

Current sensing amplifier 360 generates a signal according to detectionvoltage Vdetect and outputs the signal to voltage setting circuit 370.

Voltage setting circuit 370 generates bias voltage VBIAS from the signalinputted from current sensing amplifier 360 and third power supplyvoltage VGG. Voltage setting circuit 370 sets bias voltage VBIAS to behigher with a decrease in detection voltage Vdetect.

As stated above, when idle current Idq1 of first transistor 101decreases due to, for example, a change in temperature, source currentIsq2 of second transistor 321 in a substantially proportionalrelationship with first transistor 101 decreases. A decrease indetection voltage Vdetect leads to an increase in bias voltage VBIAS,and source current Isq2 of second transistor 321 increases. Idle currentIdq1 of first transistor 101 in the substantially proportionalrelationship with second transistor 321 also increases. Consequently,bias circuit 320 is capable of operating to increase idle current Idq1of first transistor 101 for power amplification when idle current Idq1decreases to be less than a predetermined current value due to themanufacturing variation or the temperature dependency etc.

Contrary to the above description, when idle current Idq1 of firsttransistor 101 increases, detection voltage Vdetect rises. Accordingly,bias voltage VBIAS drops, and it is possible to decrease idle currentIdq1 of first transistor 101. Consequently, bias circuit 320 is capableof controlling bias voltage VBIAS according to an increase or decreasein idle current Idq1 of first transistor 101 for power amplification, tokeep idle current Idq1 constant.

As stated above, as with Embodiment 1, since power amplifier device 300according to Embodiment 3 includes bias circuit 320 capable of reducinga variation in drain current due to a manufacturing variation ortemperature dependency of first transistor 101 for power amplification,and is further capable of reducing a supply voltage to bias circuit 320,it is possible to achieve a circuit configuration capable of powerconsumption reduction and cost reduction. Moreover, first power supplyvoltage VDD is applied to the drain of second transistor 321 in the samemanner as the drain of first transistor 101, and there is nocharacteristic difference due to drain voltage dependency. For thisreason, it is possible to reduce a variation in drain current withhigher accuracy. Furthermore, since there is no necessity to set asupply voltage to bias circuit 320 in consideration of the drain voltagedependency, it is possible to further decrease second power supplyvoltage VBB. In addition, since a low-voltage, high-precision amplifiercan be used for current sensing amplifier 360, decreasing source currentIsq2 by reducing the gate width of second transistor 321 makes itpossible to reduce power consumption.

It should be noted that although bias circuit 320 that applies biasvoltage VBIAS to the gate of second transistor 321 in the same manner asfirst transistor 101 has been described in the present embodiment, biasvoltage VBIAS may be shifted and applied. For example, FIG. 9 shows biascircuit 320 a including a level shift circuit. Bias circuit 320 aincludes level shift circuit 380 and applies a voltage obtained byshifting bias voltage VBIAS to the gate of second transistor 321. Levelshift circuit 380 outputs, for example, a voltage obtained by adding 0.1V to bias voltage VBIAS. To put it another way, the gate voltage ofsecond transistor 321 is higher than the gate voltage of firsttransistor 101 by 0.1 V. On the other hand, since current sensingresistor 322 increases a source voltage of second transistor 321 byapproximately 0.1 V, the gate-source voltage of second transistor 321substantially matches the gate-source voltage of first transistor 101.Accordingly, level shift circuit 380 is capable of reducing theinfluence of current sensing resistor 322 on a gate-source voltage.

It should be noted that although second transistor 321 has the drainconnected to the VDD terminal, and first power supply voltage VDD isapplied to the drain in the same manner as first transistor 101 in thepresent embodiment, a voltage different from the voltage applied tofirst transistor 101, such as second power supply voltage VBB, may beapplied to the drain.

As described above, power amplifier device 300 according to Embodiment 3includes: a first power supply terminal for inputting first power supplyvoltage VDD; first transistor 101 for power amplification that includesa first drain supplied with power from the first power supply terminal,a first source that is grounded, and a first gate for inputting aradio-frequency signal; a second power supply terminal for inputtingsecond power supply voltage VBB lower than first power supply voltageVDD; and bias circuit 320 that applies a bias voltage to the first gateof first transistor 101. Bias circuit 320 includes: second transistor321 for monitoring that (i) includes a second drain supplied with powerfrom the first power supply terminal or the second power supplyterminal, a second source that is substantially grounded, and a secondgate electrically connected to the first gate, and (ii) causes a sourcecurrent to flow through the second source, the source currentcorresponding to a drain current of first transistor 101; and biasadjustment circuit 350 that is supplied with power from the second powersupply terminal and adjusts the bias voltage according to the sourcecurrent of second transistor 321.

With this configuration, it is possible to reduce the power consumptionof bias circuit 320. In addition, it is possible to reduce costs becausebias circuit 320 can be formed of a low-withstand-voltage,general-purpose, low-cost element.

Here, second transistor 321 may be supplied with the power from thefirst power supply terminal.

With this configuration, second transistor 321 for monitoring is capableof operating at the first power supply voltage in the same manner asfirst transistor 101, reducing the characteristic difference betweensecond transistor 321 and first transistor 101, and improving theaccuracy of monitoring, that is, the accuracy of imitating.

Embodiment 4

Next, a power amplifier device according to Embodiment 4 will bedescribed with reference to FIG. 10.

Embodiment 4 describes a Doherty power amplifier device includingtransistors for power amplification. It should be noted that descriptionoverlapping Embodiment 1 will be omitted.

FIG. 10 is a circuit diagram illustrating one configuration of a poweramplifier device according to Embodiment 4. Power amplifier device 400shown by FIG. 10 differs from power amplifier device 100 t according toEmbodiment 1 shown by FIG. 3 in including transistors for poweramplification etc. The following mainly describes the differences.

Power amplifier device 400 has an IN terminal, an OUT terminal, a VDDterminal, a VBB terminal, a VGG terminal, and a GND terminal andincludes, for example, first semiconductor substrate 490, secondsemiconductor substrate 491, current sensing resistor 422, andquarter-wavelength phase lines 406 and 416. Some of elements (atransistor for monitoring a drain current of a transistor for poweramplification, a current sensing resistor, a bias adjustment circuit)constituting a bias circuit are separately disposed on firstsemiconductor substrate 490 and second semiconductor substrate 491.Moreover, first semiconductor substrate 490 and second semiconductorsubstrate 491, together with current sensing resistor 422, capacitors402, 405, 412, and 415, inductors 403, 404, 413, and 414,quarter-wavelength phase lines 406 and 416, are mounted on a submountsubstrate such as a multi-layer resin substrate to form power amplifierdevice 400.

First semiconductor substrate 490 has a VG_CA terminal, a VG_PAterminal, a VG2 terminal, a VD_CA terminal, a VD_PA terminal, a VD2terminal, and first transistor 401, second transistor 421, and thirdtransistor 411 are disposed on first semiconductor substrate 490. Firsttransistor 401 has, for example, gate width Wg1 of 3 mm. Secondtransistor 421 has, for example, gate width Wg2 of 0.4 mm. Thirdtransistor 411 has, for example, gate width Wg3 of 4.8 mm. Thesetransistors have the same device architecture.

Second semiconductor substrate 491 has a Vbb terminal, a Vbd terminal, aVgg terminal, a VBIAS_CA terminal, and a VBIAS_PA terminal. Currentsensing amplifier 460, voltage setting circuit 470, and level shiftcircuit 480 are disposed on second semiconductor substrate 491 to form abias adjustment circuit.

The connection of the above-described constituent elements as shown byFIG. 10 allows power amplifier device 400 to form a Doherty amplifierdevice including first transistor 401 as a carrier amplifier and thirdtransistor 411 as a peak amplifier.

The IN terminal is connected to the gate of first transistor 401 viacapacitor 402 and connected to the gate of third transistor 411 viaquarter-wavelength phase line 416 and capacitor 412.

The OUT terminal is connected to the drain of first transistor 401 viaquarter-wavelength phase line 406 and capacitor 405 and connected to thedrain of third transistor 411 via capacitor 415.

First transistor 401 performs, for example, class A or class ABoperation and always amplifies an RF input signal inputted from the INterminal. In contrast, third transistor 411 performs, for example, classC operation and amplifies an RF input signal when the RF input signalhas at least predetermined power.

The following describes operations of the power amplifier device thusconfigured according to Embodiment 4, mainly focusing on the differencesfrom Embodiment 1.

Second transistor 421, current sensing resistor 422, current sensingamplifier 460, and voltage setting circuit 470 constitute a bias circuitequivalent to bias circuit 120 shown by FIG. 1A, and the bias circuitgenerates CA bias voltage VBIAS_CA equivalent to bias voltage VBIASshown by FIG. 1A. CA bias voltage VBIAS_CA is, for example,approximately −2.5 V. CA bias voltage VBIAS_CA is applied to the gatesof first transistor 401 and second transistor 421. Accordingly, as withEmbodiment 1, by monitoring idle current Idq1 of first transistor 401and adjusting CA bias voltage VBIAS_CA, it is possible to reduce avariation in idle current Idq1 due to a manufacturing variation ortemperature dependency and to cause the power amplifier device toperform a predetermined class operation.

PA bias voltage VBIAS_PA to which CA bias voltage VBIAS_CA is shifted bylevel shift circuit 480 is applied to the gate of third transistor 411.PA bias voltage VBIAS_PA is, for example, approximately −3.5 V.Accordingly, third transistor 411 is gate-biased at PA bias voltageVBIAS_PA linked to CA bias voltage VBIAS_CA and is allowed to perform apredetermined class operation. Since third transistor 411 is disposed onsame first semiconductor substrate 490 as first transistor 401, as withfirst transistor 401, third transistor 411 is capable of reducing avariation in characteristics due to the manufacturing variation or thetemperature dependency.

As stated above, as with Embodiment 1, since power amplifier device 400according to Embodiment 4 includes the bias circuit capable of reducinga variation in drain current due to the manufacturing variation ortemperature dependency of first transistor 401 for power amplification,and is further capable of reducing a supply voltage to the bias circuit,it is possible to achieve a circuit configuration capable of powerconsumption reduction and cost reduction. Moreover, even when a poweramplifier device includes transistors for power amplifier as with poweramplifier device 400 including first transistor 401 and third transistor411, one bias adjustment circuit disposed on second semiconductorsubstrate 491 is capable of gate bias.

It should be noted that although the one bias adjustment circuitdisposed on second semiconductor substrate 491 generates CA bias voltageVBIAS_CA and PA bias voltage VBIAS_PA in the present embodiment, twodifferent bias adjustment circuits may generate CA bias voltage VBIAS_CAand PA bias voltage VBIAS_PA, respectively.

It should be noted that although first transistor 401, second transistor421, and third transistor 411 are disposed on first semiconductorsubstrate 490 in the present embodiment, third transistor 411 may bedisposed on another semiconductor substrate. In this case, thirdtransistor 411 may be contained in one package. Moreover, secondtransistor 421 may be disposed adjacent to first transistor 401.

It should be noted that although the Doherty amplifier device has beendescribed as the power amplifier device including the transistors forpower amplification in the present embodiment, the power amplifierdevice may be a power amplifier device other than the Doherty amplifierdevice. For example, the power amplifier device may be a power amplifierdevice in which transistors for power amplification are connected inseries, and a bias voltage generated by one bias adjustment circuit maybe applied to the gates of at least two transistors among transistorsfor power amplification in each stage.

As described above, power amplifier device 400 according to Embodiment 4includes a plurality of transistors for power amplification includingfirst transistor 401, and the bias circuit applies the bias voltage to agate of at least one of the plurality of transistors for poweramplification.

With this configuration, one bias circuit is capable of adjusting a biasvoltage for the transistors for power amplification.

Here, the bias circuit may generate different bias voltages for theplurality of transistors for power amplification.

With this configuration, one bias circuit is capable of supplying andadjusting different bias voltages for the transistors for poweramplification.

The accompanying drawings and detailed description are provided above asembodiments in order to describe examples of the technique disclosed inthe present application.

Therefore, the constituent elements described in the accompanyingdrawings and detailed description may include not only constituentelement necessary for solving the problem but also constituent elementsfor illustrating the technique, which are not essential to solving theproblem. For this reason, description of these non-essential constituentelements in the accompanying drawings and detailed description is notintended to acknowledged essentiality of these non-essential constituentelements.

It should be noted that the technique in the present disclosure is notlimited to these examples, and can also be applied to embodiments inwhich modifications, replacements, additions, and omissions have beenmade. Moreover, forms obtained by making, to the embodiments, variousmodifications conceived by a person skilled in the art as well as formsrealized by combining the constituent elements in the embodiments areincluded within the scope of the technique in the present disclosure,provided that these do not depart from the essence of the technique inthe present disclosure.

INDUSTRIAL APPLICABILITY

Since the power amplifier devices described in the present disclosureeach include a bias circuit capable of reducing a variation in draincurrent due to a manufacturing variation or temperature dependency of atransistor for power amplification, and are each capable of reducing asupply voltage to the bias circuit, it is possible to achieve a circuitconfiguration capable of power consumption reduction and cost reduction.

Moreover, the power amplifier devices described in the presentdisclosure can be used for, for example, power amplification systems formobile phone base stations, satellite communication base stations,mobile phone terminals, and satellite communication terminals, radartransmitters, wireless power transmitters, microwave heating devicessuch as microwave ovens.

The invention claimed is:
 1. A power amplifier device comprising: afirst power supply terminal for inputting a first power supply voltage;a first transistor for power amplification that (i) includes a firstgate to which a bias voltage is applied, and (ii) is supplied with powerfrom the first power supply terminal; a second power supply terminal forinputting a second power supply voltage lower than the first powersupply voltage; a second transistor for monitoring that (i) includes asecond gate to which the bias voltage is applied, (ii) is supplied withpower from the first power supply terminal or the second power supplyterminal, and (iii) imitates an operation of the first transistor; and abias circuit that is supplied with power from the second power supplyterminal and generates and adjusts the bias voltage according to a draincurrent or a source current of the second transistor.
 2. The poweramplifier device according to claim 1, wherein the second transistor issupplied with the power from the second power supply terminal.
 3. Thepower amplifier device according to claim 1, wherein the bias circuitgenerates and adjusts the bias voltage according to the source currentof the second transistor.
 4. A power amplifier device comprising: afirst power supply terminal for inputting a first power supply voltage;a first transistor for power amplification that includes a first drainsupplied with power from the first power supply terminal, a first sourcethat is grounded, and a first gate for inputting a radio-frequencysignal; a second power supply terminal for inputting a second powersupply voltage lower than the first power supply voltage; and a biascircuit that applies a bias voltage to the first gate of the firsttransistor, wherein the bias circuit includes: a second transistor formonitoring that (i) includes a second drain supplied with power from thesecond power supply terminal, a second source that is grounded, and asecond gate electrically connected to the first gate, and (ii) causes asecond drain current to flow through the second drain, the second draincurrent corresponding to a first drain current flowing through the firstdrain; and a bias adjustment circuit that is supplied with the powerfrom the second power supply terminal and adjusts the bias voltageaccording to the second drain current.
 5. The power amplifier deviceaccording to claim 2, wherein the second power supply voltage is set toa voltage at which the second transistor operates in a saturationregion.
 6. A power amplifier device comprising: a first power supplyterminal for inputting a first power supply voltage; a first transistorfor power amplification that includes a first drain supplied with powerfrom the first power supply terminal, a first source that is grounded,and a first gate for inputting a radio-frequency signal; a second powersupply terminal for inputting a second power supply voltage lower thanthe first power supply voltage; and a bias circuit that applies a biasvoltage to the first gate of the first transistor, wherein the biascircuit includes: a second transistor for monitoring that (i) includes asecond drain supplied with power from the first power supply terminal orthe second power supply terminal, a second source that is substantiallygrounded, and a second gate electrically connected to the first gate,and (ii) causes a source current to flow through the second source, thesource current corresponding to a drain current of the first transistor;and a bias adjustment circuit that is supplied with power from thesecond power supply terminal and adjusts the bias voltage according tothe source current of the second transistor.
 7. The power amplifierdevice according to claim 1, wherein the second transistor is suppliedwith the power from the first power supply terminal.
 8. The poweramplifier device according to claim 1, wherein the second transistor iscontained in a same package as the first transistor.
 9. The poweramplifier device according to claim 1, wherein the second transistor isdisposed on a same first semiconductor substrate as the firsttransistor.
 10. The power amplifier device according to claim 1, whereinat least part of the bias circuit is disposed on a differentsemiconductor substrate from the second transistor.
 11. The poweramplifier device according to claim 10, comprising: a current sensingresistor connected to a drain or a source of the second transistor; anda submount substrate on which the semiconductor substrate is mounted,wherein the current sensing resistor is mounted on the submountsubstrate.
 12. The power amplifier device according to claim 1,comprising: an enable control terminal for controlling an active stateand an inactive state of the bias voltage.
 13. The power amplifierdevice according to claim 1, wherein the first transistor and the secondtransistor are each a nitride semiconductor device.
 14. The poweramplifier device according to claim 1, wherein the first transistor andthe second transistor are each a laterally-diffused metal-oxidesemiconductor (LDMOS) transistor.
 15. The power amplifier deviceaccording to claim 1, comprising: a plurality of transistors for poweramplification including the first transistor, wherein the bias circuitapplies the bias voltage to a gate of at least one of the plurality oftransistors for power amplification.
 16. The power amplifier deviceaccording to claim 15, wherein the bias circuit generates different biasvoltages for the plurality of transistors for power amplification. 17.The power amplifier device according to claim 2, wherein the biascircuit generates and adjusts the bias voltage according to the sourcecurrent of the second transistor.
 18. The power amplifier deviceaccording to claim 4, wherein the second power supply voltage is set toa voltage at which the second transistor operates in a saturationregion.
 19. The power amplifier device according to claim 6, wherein thesecond transistor is supplied with the power from the first power supplyterminal.